1. Field of the Invention
This invention relates to a quality control device that can be used in a printing process and, more particularly, to a device for indicating a quantitative change in dot area of an image in a printing process and the method of making the same.
2. Description of the Prior Art
It is common practice in the graphic arts industry to use quality control devices as targets for measuring dot gain or dot loss by using various commercially available transmission and reflection densitometers. These quality control devices normally require a field of measurement of at least 0.125 inch in diameter to accommodate the field of view on commercially available densitometers. Other various quality control devices are known which indicate dot gain or dot loss in a qualitative mode to provide a subjective and relative and not an absolute measurement of dot gain or dot loss. Normally, most commercially available visual quality control devices for providing a subjective measurement of dot gain or dot loss generally require at least a 0.125 inch diameter field of view to be effective.
Other quality control devices are known for monitoring the dimensions of an image in a printing process. For example, German Auslegeschrift No. 2,401,672 to Brunner discloses a device for monitoring the dimensions of an image to be processed in a reproduction and printing process and a method for making the disclosed device. Brunner's device for monitoring the dimensions of an image composed of screen dots includes at least one measuring element provided on a substrate and includes at least one measuring symbol which permits conclusions to changes of the image during the printing process. The measuring symbol is designed so that the disappearance of a portion thereof directly constitutes a measure of the relative decrease in area of the screen dots of the image. Brunner's device may also include a second measuring symbol arranged adjacent to the aforementioned measuring symbol and being complementary thereto such that the disappearance of the second measuring symbol of the pair of measuring symbols is a measure of the relative increase in area of the screen dots.
U.S. Pat. No. 4,183,659 to Brunner discloses a means for controlling the change of thickness of lines of photographically produced briefs which are produced by the agency of a means for photographic reproduction. A control area means is provided including at least two area element means, whereby the smallest width of which and the smallest mutual distance of which correspond to the tolerance of the thickness of lines of a print.
U.S. Pat. No. 4,143,967 to Wicker discloses a method of producing an invisible photograph, latent in form, by the use of a dark screen and a method of viewing the photograph either by utilizing the same dark screen, or by making a print of the photograph by an offset printing process and then appropriately reproducing the print. Wicker's invention describes a method of halftone photography which uses an extremely dark screen to produce a halftone having micro-miniaturized positive dots containing a negative and a positive halftone image separated by a difference of 30.degree.. This separation renders the visible halftones invisible or latent.
U.S. Pat. No. 3,202,045 to Arsenault et al. discloses an apparatus for simultaneously recording space data and code on a single frame of photographic film. Arsenault's invention discloses a means by which a document may be recorded in one area on a frame of film and a block of code identifying the document may be recorded in a second defined area on the frame of film alongside the first.
U.S. Pat. No. 3,220,301 to Koonz et al. discloses a coding and photographic device and relates to the filing and retrieval of documentary information. Koonz et al. discloses an information storage medium in the form of a card or film having an area adapted to store printed information in reduced form and another area having groups of visually readable characters displayed thereon with each character having aligned therewith an area displaying a machine readable code.
U.S. Pat. No. 3,212,395 to Bailey discloses a camera digital display. Bailey's invention relates to the filing and retrieval of documentary information and to an apparatus for recording information on a storage medium. The purpose of the device in Bailey is to produce a reduced size photographic film of documents together with coding for operating suitable photoelectric sensing means to allow machine filing and retrieval using the coding.
U.S. Pat. No. 3,393,618 to Baker discloses a printing control. Baker discloses a stencil for use in preparing printing plates and for use in controlling the quality of the plates and resultant prints therefrom. The stencil has a light transmitting image to provide on the plates or prints therefrom a monotone reference indication or comparable patterns with the monotone reference indication indicating a predetermined plate or print quality and the comparable patterns indicating plate or print quality differing from the predetermined quality.
The publication Research Progress published by the Graphic Arts Technical Foundation in the article "The GATF Dot Gain Scale" by Frank Preucil et al., number 69, pp. 1-4 (November, 1965) discusses the Graphic Arts Technical Foundation Dot Gain Scale. This Dot Gain Scale is described as a visual device made up of ten steps graduated in density in the form of numbers from 0-9 designed to give numerical values to dot sharpening or dot gain. Dot area changes are indicated by the displacement of an "invisible number" to a higher or lower value.
What is needed, therefore, is a visual quality control device, under appropriate magnification, that can be used in a printing process, such as a halftone printing process, to quantitatively determine changes in dot area. What is further needed is a device for indicating a quantitative change in dot area of an image in a printing process that requires an area generally significantly smaller than the area needed by various available commercial dot gain devices to measure dot gain or loss using densitometric or visual methods. What is also needed is a microsize device which is not readily visible at normal viewing distances which can serve to protect against illegal copying or reproduction of original documents that are not to be duplicated or reproduced. What is additionally needed is a device and method for easily and accurately determining a specific quantitative change in dot area.